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International Journal of Bioprinting Cellular metamaterial flexure joints

bending motion. In soft robotic hands with MFJs, due to hand in such a way that their stiffness behavior is similar
the structurally programmable variable stiffness of the in a specific range of the bending motion and then it will be
joints, it can perform more complex in-hand manipulation different. As a result, the trajectory of the object is similar
tasks. Since the bending stiffness varies at different range to the fingers with conventional flexure joints (Figure 4A)
of the bending motion, the object will follow different up to the range that the stiffness values are similar
trajectory at different range of the joint bending angles and then it will produce different trajectory due to the
similar to externally stimulated soft actuators with variable variation in stiffness values. For this purpose, we consider
stiffness . To demonstrate this capability of the MFJs, a the first finger joints with the geometrical parameters of
[23]
two-fingered soft robotic hand with conventional and MFJ L = 25 mm, t = 0.5 mm, and θ = 60° and the second finger
s is used for in-hand manipulation of a wooden cube. with re-entrant angle is 50°, and all the other parameters
are the same. The stiffness behavior of these two joints
As shown in Figure 4A and Videoclip S1, in the robotic is shown in Figure 3C where they have similar stiffness
hand with conventional flexure joints, the joints of both at the first 15 degrees of the bending angle and then the
fingers are the same. Therefore, after grasping the wooden joint with re-entrant angle of 50° has higher stiffness. With
cube, it will move in approximately vertical direction. For this architecture of the fingers, as shown in Figure 4B and
the robotic hand with MFJs, different architecture of the Videoclip S1, from the time lapse 1 to 6, the trajectory
joints is used in the left and right fingers of the robotic is similar to the robotic hand with conventional flexure

A B

C

E G

D

F

Figure 5. Demonstration of metamaterial flexure joints (MFJs) with large bending angle through grasping linear objects. (A) How human hand grasps
linear objects; (B) trajectory of the soft robotic finger with three MFJs with different geometrical parameters; (C) close-up image of a soft robotic finger
with large bending angle of the proximal interphalangeal joint grasping a 0.3-mm wire; (D) grasping a fishing line with diameter of 0.6 mm; (E) pulling
the blind rope with a diameter of 2 mm; (F) grasping and striping a wire with diameter of 0.3 mm; and (G) holding a rope with 3 mm diameter with a 1-kg
weight attached to that.

Volume 9 Issue 3 (2023) 406 https://doi.org/10.18063/ijb.696